Boreal burning

Wildfire burns in the boreal forest of Canada's Northwest Territory July 14.

NWTFIRE

Canada's Northwest Territories are on fire. The region is experiencing its hottest, driest summer in 50 years, and wildfire activity is more than six times the 25-year average. While blazes in sparsely populated northern Canada have a minimal impact on human safety and infrastructure, they have an outsized effect on the environment: The ancient, stunted boreal forests, or taiga, ringing the Arctic Circle contain 30 percent of the world's land-based carbon.

The taiga is well adapted to fire, but a 2013 study of charcoal records shows that lately, it's been burning at rates not seen for 10,000 years. Most carbon emissions come from the tundra-like peat of the forest floor; carbon from peat fires could equal up to 40 percent of that emitted by global fossil fuels. Worse, soot from such fires can darken Arctic ice, making it melt faster.

If increased global warming spurs ever-greater fires in the taiga of Alaska, Canada and Russia, as some scientists predict, it could create a feedback loop, in which more boreal fires lead to more warming, and more warming to more fire.

Sources: The Proceedings of the National Academy of Sciences, 2013; Canadian Interagency Forest Fire Centre Situation Report; University of Guelph, Ontario; Mike Flannigan, wildland fire professor, University of Alberta